Since a photographic method of using a silver halide is superior to any other photographic methods such as an electro-photographic method or a diazo-photographic method in terms of photographic characteristics such as sensitivity and gradation adjustment, it has heretofore been utilized most widely in the technical field. Recently, the technology for simply and rapidly obtaining a photographic image has been developed by exchanging the conventional wet processing treatment with a developer or the like in a method of forming a photographic image in a silver halide-containing photographic material for a dry processing treatment by heating or the like. In particular, color hard copies with a very high image quality can be obtained by this type of such silver halide photography. This type of photography is being studied and developed.
Heat-developable diffusion transfer color photographic materials are known in this technical field, and various heat-developable diffusion transfer color photographic materials and various processes of processing the photographic materials are described, for example, in Syashin Kouqaku no Kiso (Bases of Photographic Engineering), pp. 553-555 (published by Coma Publishing Co., Ltd., 1979), Eizou Jyoho (Picture Information), page 40 (published in April, 1978); Nebletts, Handbook of Photography and Reprography, 7th Ed., pages 32 to 33 (published by Van Nostrand Reinhold Company); U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020 and 3,457,075; British Patents 1,131,108 and 1,167,777; and Research Disclosure, No. 17029 (June, 1978; RD-17029), pages 9 to 15.
Recently, business image appliances, electronic still cameras, videos and facsimiles have been popularized by the development of office automation and, accordingly, the need for graphics has increased. In particular, with development of computer graphics as well as development and progress of image sensor technology and digital processing technology, the demand for obtaining color hard copies from image information in the form of electric signals is increasing.
Conventional color photographic materials generally have color sensitivity to blue, green and red. In order to form images on such color photographic materials from image information in the form of electric signals, a color CRT (cathode ray tube) may be used as a light source for exposure. However, a CRT is unsuitable for obtaining large-size prints.
Useful writing heads for the purpose of obtaining large-size prints include a light emission diode (LED) and a semiconductor laser. However, these opto-writing heads cannot emit blue light efficiently.
Therefore, for example, if light emission diodes (LED) are used, a color photographic material having three layers each as color-sensitized to near infrared, red and yellow colors, separately, must be exposed with a light source having a combination of three light emission diodes each emitting a near infrared ray (800 nm), a red ray (670 nm) and an yellow ray (570 nm), separately. Image recording systems are described in Nikkei New Material (issued Sep. 14, 1987), pages 47 to 57, and some have been put into practical use.
For example, a system of recording a color photographic material having three light-sensitive layers each having a different color sensitivity with a light source composed of three semiconductor lasers each respectively emitting a ray of 880 nm, 820 nm, and 760 nm, correspondingly to the three light-sensitive layers of the material, is described in JP-A 61-137149 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
A system of simply and rapidly obtaining a photographic image has been developed in accordance with the needs pertaining to color hard copies, by converting the conventional wet processing treatment with a developer or the like in a method of forming a photographic image in a silver halide-containing photographic material into an instant photographic system containing a developer in the photographic material itself or into a dry heat-development processing treatment by heating or the like. In the simple and rapid processing method, an image forming system by diffusion transfer process is frequently employed for the purpose of preventing stains of the printed images, which often occur during the printing-out step of the developed silver halide materials.
A diffusion transfer method involves a diffusive dye which is imagewise formed or released and the diffusive dye which is transferred to an image-receiving material having a mordant agent with water or a solvent. The details of this type of method are described in Angew. Chem. Int. Ed. Engl., 22 (1983), 191.
The present invention is directed to diffusion transfer color photographic materials, which can be used when a color photographic material which may be applied to the above-mentioned writing heads (e.g., semiconductor laser and LED).
In order to achieve the above-mentioned color photographic material, it is necessary to select a three-color light source having a spectral wavelength distribution essentially in an infrared range of 600 nm or more and in a narrow wavelength range. Therefore, planning the spectral sensitivity of silver halides used in the photographic material is extremely difficult. Accordingly, a method of separating the plural color sensitivities of the material with filter dyes as incorporated therein or of sharpening the color sensitivities of the material with them has been employed in this technical field. The method has been described in U.S. Pat. No. 4,619,892 where the short wave length sensitivity of the two color sensitivities is elevated or filter layers are introduced into the photographic material.
The present applicant also investigated the method of using filter dyes. However, the filter dyes which are used in color papers in this technical field are soluble in water since they must be decolored after processing. If such water-soluble dyes are used in diffusion transfer color photographic materials, they would inconveniently and disadvantageously be transferred to image-receiving materials. Therefore, such water-soluble dyes cannot be used in diffusion transfer color photographic materials.
Consequently, introduction of an oil-soluble ballast group into filter dyes for the purpose of oil-protecting emulsification has been tried. However, when only this type of filter dye is emulsified and dispersed singly, it has been found that the half-value width of the peak of the color absorption is broadened because of the side-absorption which is possibly caused by an aggregate of the dye so that the intended color separation could not be attained. In addition, it has also been found that in the photographic material containing the emulsified dispersion of the filter dye, the filter dye is decomposed during storage of the raw film of the material.
The object of the present invention is to provide a diffusion transfer color photographic material having excellent color separability and color image discrimnability and also having excellent raw film storability. The "raw film storability" referred to herein means that the photographic properties of the raw photographic material do not significantly vary or fluctuate after the material has been stored for a long period of time of several months or more.
In addition, where a multi-layer color photographic material is exposed to three different spectral ranges to thereby separately form yellow, magenta and cyan colors therein, it is an important technique for color reproduction to separately form the respective colors without color mixing them.
In particular, where a light emission diode (LED) or a semiconductor laser (LD) is used as a light source for exposure of the material, it is inevitable to plan the three color sensitivities in a narrow spectral range in preparing the multi-layer color photographic material. The key is how to reduce the overlap of the respective color sensitivities with each other to improve the color separability of the material.
A method which meets this requirement, for example, is described in U.S. Pat. No. 4,619,892 which mentions stepwise elevation of the sensitivities in the short wavelength range and introduction of filter dyes in the photographic material.
However, it has been found that elevation of the sensitivities in the short wavelength range to ensure color separability of a multi-layer color photographic material defectively causes increase of Dmin which, in turn, adversely affects the time-dependent raw film storage stability.
In addition, where the photographic material is to have a difference in sensitivities as mentioned above, the problem arises where that the development characteristics of the respective light-sensitive layers differ from each other. In other words, the respective light-sensitive layers in the material would have different dependence on temperature and water amount for development so that the time-dependent fluctuation (in-day fluctuation and day-to-day fluctuation) of the color evenness and color balance in the picture plane of the material would be large defectively.
Accordingly, another object of the present invention is to provide a multi-layer heat-developable diffusion transfer color photographic material having excellent time-dependent raw film storage stability.
Still another object of the present invention is to provide a diffusion transfer color photographic material which may be developed with little dependence on temperature and water amount, which has excellent sharpness and which may be produced at a low manufacturing cost.